Microsoft Outlook mobile app
Microsoft's mobile Outlook app allows you to access shared calendars easily. For the latest and most accurate information, please visit Microsoft's website at https://support.microsoft.com/en-us/office/how-do-i-open-a-shared-calendar-d8011619-eaa1-4459-8417-223bfc5ca0c2.
Native iOS and iPadOS apps
It is not possible to access a shared calendar using the native Calendar app.
The TechMail system runs Microsoft Exchange Online (through Microsoft 365). The ActiveSync technology built into Exchange Online which allows mobile device access from third parties like Apple does not contain support for accessing shared folders. ActiveSync is what Apple's mobile devices use to access Exchange Online through the native apps, and therefore it's not possible to access a shared mailbox using the native apps (Mail, Calendar, Contacts, Reminders, and Notes) on your iPhone or iPad.
Third-party apps may be available from the App Store which allow you to access shared calendars. Search the App Store for the latest information.